This invention relates to a servo control apparatus for driving a machine tool, etc., and in particular to a servo control apparatus for suppressing a periodical disturbance.
FIG. 10 is a control block diagram of a servo control apparatus comprising a periodical disturbance corrector in a speed control loop for the purpose of correcting in a system to which a periodical disturbance is added in a related art.
In FIG. 10, numeral 1 denotes a position command generation section, numeral 2 denotes a position control section, numeral 3 denotes a speed control section, numeral 4 denotes a current control section, numeral 5 denotes a power amplification circuit, numeral 6 denotes a servomotor for driving a machine system, numeral 7 decodes an encoder or detecting the rotation position of the servomotor 6, and numeral 8 denotes differentiating means for differentiating a position detection signal output by the encoder 7 to calculate speed. The encoder 7 and the differentiating means 8 make up motor speed detection means. Numeral 9 denotes a position command output from the position command generation section 1, numeral 10 denotes a position feedback signal output from the encoder 7, numeral 11 denotes a speed command output from the position control section 2, numeral 12 denotes a speed detection signal (speed feedback signal) output from the differentiating means 8, numeral 13 denotes a speed deviation signal of the difference between the speed command 11 and the speed detection signal 12, numeral 14 denotes a current command output from the speed control section 3, numeral 15 denotes a current command to which a correction value 20 output through a periodical disturbance corrector 19 is added, numeral 16 denotes a current feedback signal indicating a current flowing into the servomotor 6, numeral 17 denotes the machine system driven by the servomotor 6, and numeral 18 denotes a periodical disturbance.
In the servo control apparatus, the position feedback signal 10 of the servomotor 6 detected by the encoder 7 follows the position command signal 9 output by the position command generation section 1 for rotating the servomotor 6. To perform this operation stably at high speed, the position control section 2 generates the speed command 11 based on a deviation signal between the position command 9 and the position feedback signal 10, and the speed control section 3 outputs the current command 14 to the servomotor 6 so that the speed feedback signal generated by the differentiating means 8 based on the position feedback signal 10 follows the speed command 11. A correction value 20 for suppressing the effect of a disturbance is added to the current command 14, and the current control section and the power amplification circuit 5 control the electric current allowed to flow into the servomotor 6 so that the current feedback signal 16 indicating the value of the current flowing into the servomotor 6 follows it.
By the way, in a machine tool, the disturbance 18 caused by motor rotation, rotation of a ball screw, or a natural frequency of machine often adversely affects cutting accuracy.
Hitherto, the responsivity of a position loop or a speed loop has been enhanced for suppressing the adverse effect and to realize it, it has been necessary to increase the gains of the position control section 2 and the speed control section 3 and increase the gain of a disturbance observer.
In the methods, however, the gains are increased in all frequency bands and there is a problem of inducing machine resonance at the natural frequency of a machine system, etc.
If the proportion constant between the disturbance frequency and the motor rotation speed is already known, the technique of adding correction value 20 to the current command 14 based on the information or the like is used as shown in FIG. 10; also in this case, the amplitude and phase of the correction amount need to be determined by previously measuring the speed waveform and the current waveform when the machine is started and measuring the cutting result. Even if an appropriate value is set at one rotation speed, the correction amount (gain) and the phase deviate due to change in the disturbance frequency caused by change in the motor rotation speed during execution of normal motor control, and no effect can be produced; this is a problem.
If fluctuation caused by the periodical disturbance 18 does not appear in the speed feedback signal 12 or the current feedback signal 16 that can be detected as the servo control apparatus and the effect of the disturbance 18 appears only at a machine end, adversely affecting the cutting accuracy, a problem of being incapable of determining the appropriate values of the amplitude and phase of the correction amount or the like occurs.
Further, also in a servo system to which the cutting disturbance 18 occurring due to the number of teeth of a tool attached to a main shaft or the disturbance 18 proportional to the rotation speed of the main shaft of a factor other than the controlled shaft such as touch rotation around the shaft such as a magnetic bearing for supporting the shaft of a spindle motor of a machine tool using an electromagnet is added, hitherto, basically the responsivity of a position loop or a speed loop has been enhanced for suppressing the adverse effect and to realize it, it has been necessary to increase the gains of the position control section 2 and the speed control section 3 and increase the gain of a disturbance observer. However, the methods involve a problem of easily inducing machine resonance at the natural frequency of a machine system, etc.
The invention is intended for solving the problems as described above and it is an object of the invention to provide a servo control apparatus capable of appropriately suppressing disturbances caused by various factors in real time.
Then, according to the invention, there is provided a servo control apparatus comprising detection means for detecting the position and speed of a servomotor, a position control section for generating a speed command based on the difference between a position command and a position feedback signal output by the above-mentioned detection means, a speed control section for generating a current command based on the difference between the above-mentioned speed command and a speed feedback signal, a current control section for controlling an electric current allowed to flow into the above-mentioned motor based on the above-mentioned current command, and a periodical disturbance estimater, if a disturbance having a frequency proportional to the rotation speed of the above-mentioned motor is loaded on (added to) a servo system containing a driven machine, the periodical disturbance estimater for inputting information of a proportionality constant between the disturbance frequency and the motor rotation speed, motor position information, and a difference signal between the above-mentioned speed command and the speed feedback signal and estimating magnitudes of a sine-wave component and a cosine-wave component at the frequency of the disturbance in real time during the normal motor driving, wherein the sine-wave component and the cosine-wave component at the frequency of the disturbance estimated are combined and the result is added to the above-mentioned current command as a correction value in real time during the normal motor driving.
Thus, if the disturbance having a frequency proportional to the motor rotation speed is loaded on (added to) the servo system containing the driven machine, the effect of the disturbance can be suppressed in real time during the normal motor driving.
According to the invention, there is provided a servo control apparatus comprising detection means for detecting the position and speed of a servomotor, a position control section for generating a speed command based on the difference between a position command and a position feedback signal output by the above-mentioned detection means, a speed control section for generating a current command based on the difference between the above-mentioned speed command and a speed feedback signal, a current control section for controlling an electric current allowed to flow into the above-mentioned motor based on the above-mentioned current command, and a periodical disturbance estimater, if a disturbance loaded on (added to) a servo system has a machine-proper fixed frequency, the periodical disturbance estimater for inputting information of the machine-proper frequency and a difference signal between the speed command and the speed feedback signal and estimating magnitudes of a sine-wave component and a cosine-wave component at the frequency of the disturbance in real time during the normal motor driving, wherein the sine-wave component and the cosine-wave component at the frequency of the disturbance estimated are combined and the result is added to the above-mentioned current command as a correction value in real time during the normal motor driving.
Thus, if the disturbance added to the servo system has the machine-proper fixed frequency, the effect of the disturbance can be suppressed.
According to the invention, there is provided a servo control apparatus comprising detection means for detecting the position and speed of a servomotor, a position control section for generating a speed command based on the difference between a position command and a position feedback signal output by the above-mentioned detection means, a speed control section for generating a current command based on the difference between the above-mentioned speed command and a speed feedback signal, a current control section for controlling an electric current allowed to flow into the above-mentioned motor based on the above-mentioned current command, and a periodical disturbance estimater, if a disturbance having a frequency proportional to the rotation speed of the above-mentioned motor is loaded on (added to) a servo system containing a driven machine, the periodical disturbance estimater for inputting information of a proportionality constant between the disturbance frequency and the motor rotation speed, motor position information, and an output signal from an external displacement sensor attached to a machine end and estimating magnitudes of a sine-wave component and a cosine-wave component at the frequency of the disturbance in real time during the normal motor driving, wherein the sine-wave component and the cosine-wave component at the frequency of the disturbance estimated are combined and the result is added to the above-mentioned current command as a correction value in real time during the normal motor driving.
Thus, if fluctuation caused by the periodical disturbance having a frequency proportional to the motor rotation speed does not appear in the speed feedback signal or a current feedback signal that can be detected as the servo control apparatus and the effect of the disturbance appears only at the machine end, adversely affecting the cutting accuracy, the effect of the disturbance can be suppressed.
According to the invention, there is provided a servo control apparatus comprising detection means for detecting the position and speed of a servomotor, a position control section for generating a speed command based on the difference between a position command and a position feedback signal output by the above-mentioned detection means, a speed control section for generating a current command based on the difference between the above-mentioned speed command and a speed feedback signal, a current control section for controlling an electric current allowed to flow into the above-mentioned motor based on the above-mentioned current command, and a periodical disturbance estimater, if a disturbance loaded on (added to) a servo system has a machine-proper fixed frequency, the periodical disturbance estimater for inputting information of the machine-proper frequency and an output signal from an external displacement sensor attached to a machine end and estimating magnitudes of a sine-wave component and a cosine-wave component at the frequency of the disturbance in real time during the normal motor driving, wherein the sine-wave component and the cosine-wave component at the frequency of the disturbance estimated are combined and the result is added to the above-mentioned current command as a correction value in real time during the normal motor driving.
Thus, if fluctuation caused by the periodical disturbance having the machine-proper fixed frequency does not appear in the speed feedback signal or a current feedback signal that can be detected as the servo control apparatus and the effect of the disturbance appears only at the machine end, adversely affecting the cutting accuracy, the effect of the disturbance can be suppressed.
According to the invention, there is provided a servo control apparatus comprising detection means for detecting the position and speed of a servomotor, a position control section for generating a speed command based on the difference between a position command and a position feedback signal output by the above-mentioned detection means, a speed control section for generating a current command based on the difference between the above-mentioned speed command and a speed feedback signal, a current control section for controlling an electric current allowed to flow into the above-mentioned motor based on the above-mentioned current command, detection means for detecting rotation speed of a main shaft, and a periodical disturbance estimater, if a disturbance proportional to the rotation speed of the main shaft is added to a servo system, the periodical disturbance estimater for inputting information of a proportionality constant between the disturbance frequency and the rotation speed of the main shaft, information of the rotation speed of the main shaft, and a difference signal between the above-mentioned speed command and the speed feedback signal and estimating magnitudes of a sine-wave component and a cosine-wave component at the frequency of the disturbance in real time during the normal motor driving, wherein the sine-wave component and the cosine-wave component at the frequency of the disturbance estimated are combined and the result is added to the above-mentioned current command as a correction value in real time during the normal motor driving.
Thus, if the disturbance added to the servomotor is a disturbance caused by the rotation speed of the spindle motor and the main shaft control apparatus controlled by the same numerical control apparatus (for example, cutting disturbance occurring due to the number of teeth of a tool attached to a main shaft or disturbance proportional to the rotation speed of the main shaft of a factor other than the controlled shaft such as touch rotation around the shaft such as a magnetic bearing for supporting the shaft of a spindle motor of a machine tool using an electromagnet), the effect of the disturbance can be suppressed.